What materials do you recommend as a coating layer to obtain liquid crystal cells with homeotropic alignment of molecules? In some articles, lecithin is mentioned, a small amount of which should be dissolved in ethanol and then coated on ito glass, but the ratio of lecithin to ethanol and how it is prepared is not discussed. If anyone has a solution or experience regarding the preparation of liquid crystal cells with homeotropic alignment of molecules, please help?
Dear Marziye Khodaee this is a very interesting technical question. As synthetic inorganic chemists we actually never worked with liquid crystals. However, I made the experience that many useful informations ahout a certain research topic can be found right here on the platform. Just search RG for the term "homeotropic alignment of liquid crystals" and then click on "Publications". You will be surprised to see how many potentially useful literature references will be displayed. Some of them are even available as public full texts:
https://www.researchgate.net/search.Search.html?type=publication&query=Homeotropic%20alignment%20of%20liquid%20crystals
I hope this helps. Good luck with your work!
Dear Frank,
Thank you very much for your response.
In fact, I found out during my research that different materials were used for this purpose. However, there are no instructions for making solvents related to these substances, and in the articles, only the name of the substance is mentioned. For example, we can refer to lecithin, which is simply said to dissolve a small amount of it in ethanol solvent, and there is no mention of the weight percentage of the compound or how it is prepared.
Bests,
Marziyeh
We usually get homeotropic cells already assembled from Instec. Spin coating can be a pain. About lecithin, here you have a number but depends on your system, your substrates, your LC, etc. If you spin coat, rotation speed, ramps, temp, gas flow, etc affects a lot, so there's a lot of trial and error involved. Even washing the glass with soap can yield homeotropic alignment for some observations (but the soap will leak into the LC). For proper work, probably poliimides + spin coat parameters optimization would be better or just buy the cells. They are quite more affordable than newport/thorlabs LC cells. You can find the book on libgen if you want to give it a read and/or follow references.
As per my knowledge polyimide is best for coating to prepare Homeotropic LC cells.
You may procure polyimide from any of these companies:
Nisaan Chemicals, Japan
HD Microsystem
Daily Poly Corp.
Dear Marziye Khodaee
Try Lecithin, which is an organic material, in IPA solvent. You may use 0.02 wt% of lecithin in IPA, this composition would provide homeotropic alignment to LC molecules.
Greetings Marziyeh,
Previously, most researches employed lecithin as an alignment agent for homeotropic alignment and nylon (6/6) reagent for homogenous alignment of LC molecules. These are good alignment agents.
However, I recommend that you use polyimide for the optimum alignment and anchoring. You can buy polyimide from any of the following companies:
HD Microsystem(USA), Daily Poly Corp. (Taiwan) or Nisaan Chemicals (Japan).
In our laboratory, we use the homogeneous polyamide (HA-PI) AL-1426CA and the vertical polyamide (VA-PI) AL-8395D (both from Daily Polymer Corp., Taiwan).
It delivers remarkable results such as polar anchoring of approximately 3*10(-4) J/m(2) and a pretilt angle of approximately 1.8 to 2 degrees for HA cells and roughly 88.7 to 89 degrees for VA cells in 5 micron cells using pure E7 liquid crystals.
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